The pigmentary response to photochemotherapy

Previous studies on skin topically photosensitized with trimethylpsoralen and subsequently irradiated with long-wave UV light have demonstrated an increase in melanosome size and changes in the distribution patterns of melanosomes, suggesting the possibility of gene derepression or the induction of a somatic mutation of melanocytes. The present investigation was performed to determine whether identical changes are induced by systemic photochemotherapy using 8-methoxypsoralen and UVA (PUVA) under therapeutic conditions. Our results show that PUVA stimulates melanogenesis but does not induce significant changes in the average size of melanosomes nor in their distribution patterns within keratinocytes. Thus they indicate that under therapeutic conditions PUVA does not induce morphologically detectable cytogenetic changes in pigment cells.